1. Field of the Invention
This invention pertains to the field of material dispensers that receive prepackaged containers of viscous material and provide a mechanical force to dispense the material from the container. Common viscous materials that are prepackaged and dispensed in this manner include silicone caulk and construction adhesives.
2. Description of the Related Art
Caulk dispensers, also referred to as caulk, or caulking, guns, are disclosed in prior art patents U.S. Pat. Nos. 5,595,327, 5,553,754, and 2,801,775. Such dispensers receive a tube of caulk and provide a trigger actuated plunger that pushes against a rear piston of the caulk tube to dispense caulk through a caulk tube nozzle.
Problematically, many prior art caulk dispensers drool caulk from the nozzle even after the dispenser operator stops actuating the plunger. Because the plunger is urged against the caulk tube piston (unless the plunger is disengaged), and because many viscous materials are compressible, caulk drools out of the nozzle even after the operator stops activating the plunger. This caulk drool can cause caulk to end up in unintended places and prevents a clean professional appearance to caulk work.
A partial work-around solution to caulk drool is to quickly disengage the plunger as soon as the operator desires to stop the flow of caulk. However, this solution requires quick two handed action--action which can be dangerous in some circumstances, such as when working on a ladder. Also, this solution does not address a problem of caulk drool while the operator temporarily ceases operation while re-cocking the dispenser trigger. Additionally, this solution is only a partial solution because many viscous materials, such as silicone caulk, are slightly compressed during the dispensing operation and continue to drool from the caulk tube even after the plunger is disengaged.
U.S. Pat. Nos. 5,595,327 and 5,553,754 disclose caulk dispensers that prevent caulk drool by coupling the plunger to the caulk tube piston and providing a spring that urges the plunger backward when the dispenser trigger is released. This backward urging and plunger--piston coupling urge the piston backward within the caulk tube thus reducing pressure within the caulk tube to prevent caulk from drooling from the nozzle after the trigger is released. Such caulk dispensers perform well to end caulk drool. Though not literally correct, this feature is often described as "dripless" in the art.
However, a problem occurs in prior art devices that have this plunger--piston coupling. Such prior art caulk dispensers have a caulk tube cradle that receives the caulk tube that includes a half-cylinder having a rear receptacle and a forward receptacle. The caulk tube is mounted in the cradle by inserting a rear end of the tube into the cradle's rear receptacle at an angle and pushing the tube fully into the rear receptacle and then swinging the caulk tube downward into the cradle while the tube nozzle is guided into a nozzle cutout in the forward receptacle. The tube is then slid forward to rest against an inside surface of the forward receptacle. When the plunger pushes against the caulk tube piston, the caulk tube is pushed forward against the forward receptacle, which receptacle prevents forward motion of the caulk tube.
To accommodate mounting the caulk tube into the cradle, the distance between the rear receptacle and the forward receptacle must be substantially greater than the length of the caulk tube. Accordingly, the caulk tube is able to slide longitudinally along the cradle between the rear receptacle and the forward receptacle.
In conventional caulk dispensers that do not have the no-drool feature, the longitudinal play of the caulk tube in the cradle is not a problem because the plunger maintains a forwardly-directed pressure on the caulk tube (which is, in part, why the caulk tube continues to drool caulk after the operator stops operation of the dispenser).
However, in caulk dispensers with the above-described no-drool feature, the plunger draws rearwardly slightly to stop caulk drool. And, if the caulk tube is able to move longitudinally in the cradle, the caulk tube moves rearwardly in response to the rearward draw of the plunger. The effect is slight, so that the no-drool feature works well when the dispenser is oriented with the caulk nozzle downward. However, when the dispenser is oriented with the nozzle upward, the caulk tube tends to slide rearwardly under the force of gravity and when the plunger withdraws slightly, the caulk tube moves rearwardly and the dispenser is made effete.
Methods to prevent the rearward motion of the caulk tube when the plunger withdraws are disclosed in U.S. Pat. Nos. 5,482,189 and 5,595,327 and include a moveable backplate that is biased fowardly against a back end of the caulk tube to resist that rearward urging of the plunger. Other methods include various devices to capture the caulk tube in the cradle, such as tube clamping collars.
While, these methods provide satisfactory service, they are not optimum for manufacturing or operation because of extra parts, additional cost, added complexity (no one expects to use an instruction sheet to load a tube of caulk into a caulk gun) and extra steps of operation. Thus, a caulk dispenser that provides no-drool operation, minimum parts and operation steps, and a substantially conventional means to install a caulk tube is desirable.
Additionally, while it is normally advantageous to have a no-drool caulk dispenser, it is sometimes desirable to have a caulk dispenser that performs conventionally. Thus, a caulk dispenser that is easily convertible from no-drool operation to conventional operation is also desirable.